pwm: atmel-tcb: Don't track polarity in driver data

struct atmel_tcb_pwm_device::polarity is only used in atmel_tcb_pwm_enable
and atmel_tcb_pwm_disable(). These functions are only called by
atmel_tcb_pwm_apply() after the member variable was assigned to
state->polarity. So the value assigned in atmel_tcb_pwm_request() is
never used and the member can be dropped from struct atmel_tcb_pwm_device.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>